Appendix II. 799
17 in. projectile, fired with 8 cwt of powder, the impression
being but if in. deep. (See j>. 976.) • < ..
Tungsten Steel (called also Musket's Steel) is also a self-
hardening steel, similarly suitable for projectiles and cutting
tools, and having a composition by analysis of—
Carbon % Tungsten °/0 Silicon °/0 Manganese °/0
1-36 2-58 -4.2 -25
Sterro Metal is a brass to which have been added small
proportions of iron and tin. Its percentage composition is—
Copper......55 to 60
Zinc ... ... 34 to 44
Iron ... ... 2 to 4
Tin ...... i to 2
It is both cheaper and stronger than gun-metal. Speaking
generally, the presence of iron reduces the tenacity, but in the
proportions shewn is of value. This metal has been used for
Delta Metal, though its proportions are unpublished, seems
to be simply Sterro metal in a forged or rolled condition. The
mechanical treatment thus received considerably increases its
strength, and it is much advocated for ship propellers. Though
the presence of iron causes a slight rust, the loss after six months'
immersion in an acid-impregnated water was but 1*2% as against
46% with wrought iron or steel.
Silicon Bronze is an alloy of copper and silicon, the latter
acting as a flux or reducing -agent, clarifying the copper and pre-
venting oxide scale. The resulting product is very strong, as
here shewn :
The second sample is deficient in toughness, and more than
5 % silicon causes great brittleness, Adding *r % of silicon to
melted copper produces clean castings by removing oxide, and a
little silicon to any brass or bronze is advisable. Silicon bronze
Breaking stress, tons so. in.